Fuente: WIPO "processing tomato" The invention discloses application of carnosic acid nano-emulsion as an agricultural bactericide for preventing and treating plant diseases. The plant diseases comprise rhizoctonia solani, colletotrichum rubrum, botrytis cinerea, peronophythora litchii, phytophthora capsici, colletotrichum gloeosporioides, tomato ralstonia solanacearum, citrus canker germs, potato soft rot germs, xanthomonas oryzae pv. Oryzae, mango bacterial angular leaf spot germs and muskmelon bacterial fruit spot germs; the carnosic acid nano-emulsion is prepared from the following raw materials in percentage by mass: 0.5 to 5 percent of carnosic acid, 5 to 20 percent of organic solvent, 4.0 to 10 percent of emulsifier and the balance of water. The carnosic acid nano-emulsion prepared by the invention has the characteristics of simplicity in processing, emulsion stability, good wettability, obvious bactericidal activity and the like, and meanwhile, the carnosic acid is a plant secondary metabolite and is high in use safety in the process of preventing and treating plant diseases.